We consider that the observed high olefin
selectivity may largely be due to the stabilization of the propyl radical by the nitroxyl radical
site. Indeed, the one-dimensional (1D) nature of
this edge avoids the creation of a highly reactive
propyl radical (typical of 0D single-site catalysts)
(34), and also the overoxidation of the adsorbed
species (typical of 2D surface catalysts) is suppressed (35). The proposed intermediate structures and energies of the overall catalytic cycle
are included in fig. S11. We envision that a
second abstraction of a hydrogen atom from a
primary carbon follows another radical rebound,
and creates a di-propoxyl intermediate. Desorption of propene and the reorganization of hydrogen atoms along the edge form water as a side
product. The desorption of water is followed by
oxygen addition to regenerate the >B–O–O–N<
active site. Similar surface reorganization of hydroxyl groups in the presence of oxygen was proposed for related carbon nanofilament catalysts
for oxidative dehydrogenation of ethylbenzene
to form styrene (36). All steps in this process,
except for desorption of propene, are exothermic.
The second-order rate dependence with respect
to PC3H8 suggests that two propane molecules
are required to generate two molecules of water,
in line with the overall stoichiometry of the
reaction. The desorption of these water molecules forms BN edge vacancies that allow for
unique O2 activation, which explains the influence that the surface coverage of adsorbed oxygen has on the rate of propane consumption.
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We thank the Wisconsin Alumni Research Foundation (WARF) for
funding through the WARF Accelerator Program. We thank S. Stahl
and J. Dumesic for their helpful feedback when reviewing this
manuscript. J. T.G., C.A.C, J.V., A.C., and I.H. are inventors on
patent application U.S. 15/260,649, submitted by the WARF,
that covers BN as catalysts for ODHP and other related
reactions. All data are reported in the main paper and
Materials and Methods
Figs. S1 to S14
Tables S1 and S2
Movies S1 and S2
29 June 2016; resubmitted 26 September 2016
Accepted 16 November 2016
Published online 1 December 2016
in superconducting qubits
by quasiparticle pumping
Simon Gustavsson,1 Fei Yan,1 Gianluigi Catelani,2 Jonas Bylander,3 Archana Kamal,1
Jeffrey Birenbaum,4 David Hover,4 Danna Rosenberg,4 Gabriel Samach,4 Adam P. Sears,4
Steven J. Weber,4 Jonilyn L. Yoder,4 John Clarke,5 Andrew J. Kerman,4 Fumiki Yoshihara,6
Yasunobu Nakamura,7,8 Terry P. Orlando,1 William D. Oliver1,4,9
Dynamical error suppression techniques are commonly used to improve coherence in quantum
systems. They reduce dephasing errors by applying control pulses designed to reverse
erroneous coherent evolution driven by environmental noise. However, such methods cannot
correct for irreversible processes such as energy relaxation. We investigate a complementary,
stochastic approach to reducing errors: Instead of deterministically reversing the unwanted
qubit evolution, we use control pulses to shape the noise environment dynamically. In the
context of superconducting qubits, we implement a pumping sequence to reduce the number
of unpaired electrons (quasiparticles) in close proximity to the device. A 70% reduction in the
quasiparticle density results in a threefold enhancement in qubit relaxation times and a
comparable reduction in coherence variability.
Since Hahn’s invention of the spin echo in 1950 (1), coherent control techniques have been crucial tools for reducing errors, improving control fidelity, performing noise spectroscopy, and generally extending co-
herence in both natural and artificial spin sys-
tems. All of these methods are similar: They
correct for dephasing errors by reversing un-
intended phase accumulations due to a noisy en-
vironment through the application of a sequence
of control pulses, thereby improving the dephasing
time T2. However, such coherent control tech-
niques cannot correct for irreversible processes that
reduce the relaxation time T1, where energy is
lost to the environment. Improving T1 requires
reducing the coupling between the spin system
and its noisy environment, reducing the noise in
the environment itself (2), or implementing full
quantum error correction. We demonstrate a
pumping sequence that dynamically reduces the
noise in the environment and improves T1 of a
superconducting qubit through an irreversible
SCIENCE sciencemag.org 23 DECEMBER 2016 • VOL 354 ISSUE 6319 1573
1Research Laboratory of Electronics, Massachusetts Institute of
Technology, Cambridge, MA 02139, USA. 2Forschungszentrum
Jülich, Peter Grünberg Institut (PGI-2), 52425 Jülich, Germany.
3Microtechnology and Nanoscience, Chalmers University of
Technology, SE-41296 Gothenburg, Sweden. 4Massachusetts
Institute of Technology (MIT) Lincoln Laboratory, 244 Wood
Street, Lexington, MA 02420, USA. 5Department of Physics,
University of California, Berkeley, CA 94720, USA. 6The Institute
of Physical and Chemical Research (RIKEN), Wako, Saitama
351-0198, Japan. 7Center for Emergent Matter Science (CEMS),
RIKEN, Wako, Saitama 351-0198, Japan. 8Research Center for
Advanced Science and Technology (RCAST), The University of
Tokyo, Komaba, Meguro-ku, Tokyo 153-8904, Japan.
9Department of Physics, Massachusetts Institute of Technology,
Cambridge, MA 02139, USA.
*Corresponding author. Email: firstname.lastname@example.org
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